A more thorough explanation:

Fief d'hauberk is a type of feudal land tenure that required the tenant to provide military service by appearing fully armed when summoned by the lord. It was considered the most honorable species of tenure and was held by knight-service. The term comes from the French word "fief" meaning "feudal land" and "hauberk" meaning "a piece of armor consisting of a shirt of mail."

• A knight is granted a fief d'hauberk by the lord in exchange for military service.
• The fief d'hauberk passed down from the knight to his eldest son.

These examples illustrate how a fief d'hauberk was a type of feudal land tenure that required military service and was passed down through inheritance.